Electro-mechanical torque control-acceleration of return motion

ABSTRACT

A method of returning an electro-mechanical axial setting device, wherein the axial setting device includes two setting rings centered on a common axis, one of which is axially held, and one of which is rotationally fixedly held in a housing. The two setting rings each include circumferentially extending grooves. Each of the grooves define a depth which rises in the circumferential direction. Pairs of grooves in the setting rings each accommodate a ball. The rotatingly drivable setting ring is connected to an electric drive motor. The axially displaceable setting ring is loaded by pressure springs towards the axially held setting ring. When applying a positive voltage to the electric motor, the axial setting device moves into an advanced position and when the voltage is disconnected from the electric motor, the axial setting device is returned into a starting position.

TECHNICAL FIELD

The present invention relates to a method and system of controlling anelectromechanical axial setting device, particularly suited for frictioncouplings.

BACKGROUND OF THE INVENTION

The invention relates to a method of returning an electro-mechanicalaxial setting device, wherein the axial setting device includes thefollowing: two setting rings centered on a common axis, one of which isaxially held, with the other one being axially displaceably mounted, andone of which is rotationally fixedly held in a housing, with the otherone being rotatingly drivable. The two setting rings, on theirrespective end faces facing one another, each include an identicalplurality of circumferentially extending grooves, the grooves, in a planview of the end faces, have depths which rise in the samecircumferential direction. Pairs of grooves in the two setting ringseach accommodate a ball. The rotatingly drivable setting ring isconnected to an electric motor in respect of drive, and the axiallydisplaceable setting ring is loaded by pressure springs towards theaxially held setting ring. When applying a positive voltage to theelectric motor, the axial setting device moves into an advancedposition, and when disconnecting the voltage from the electric motor,the axial setting device returns into a starting position.

Furthermore, the invention relates to an electromechanical axial settingdevice for carrying out the inventive method.

Axial setting devices of the foregoing type have a simple and compactdesign and comprise short reaction times, such as they are required, forexample, in friction couplings in locking differentials. The use of suchsetting devices is described in DE 39 20 861 C2, DE 39 15 959 C2, DE 3909 112 C2, DE 38 15 225 C2 and DE 100 33 482.2. In these publications,it is mentioned several times that to make locking differentialscomprising such setting devices compatible with vehicles provided withABS systems and/or ESP systems, it must be possible for such axialsetting devices to be returned quickly. Such a return motion is achievedby return springs. When in the form of spiral springs, they rotate therotated setting ring backwards directly and thus allow the axiallydisplaced setting ring to return. When in the form of axial springs,with groove assemblies without self-inhibition, they push back theaxially displaced setting ring and thus rotate the rotated setting ringbackwards.

To accelerate the return motion, a negative voltage may be applied tothe electric motor for returning purposes. The results of this returningmethod are still unsatisfactory and have to be improved further in orderto achieve accelerated control cycles.

One method for returning the electric motor requires that, first, anegative voltage is applied to the electric motor, and when the electricmotor has reached its idling speed, it is disconnected from the voltage.

By way of the control strategy described herein it is possible to save agreat deal of time as compared to the simple passive return motioninitiated by spring force in that, especially during the accelerationphase, the spring force is supported by the drive effected by theelectric motor. Surprisingly, time is also saved as compared to apermanently applied negative voltage during the return motion, theeffect of which permanently applied negative voltage is counteracted bythe induced counter voltage if the idling speed is exceeded.

Another embodiment in accordance with the invention includes a voltagereversing circuit for the electric motor and a motor speed recordingdevice for the electric motor which are logically connected to oneanother via the idling speed of the electric motor in such a way thatthe voltage reversing circuit is disconnected if, in the course of thedevice being returned, the idling speed of the electric motor isreached.

To be able to determine the point in time at which the negative voltageat the electric motor is interrupted, it is possible to use direct speedmonitoring means. However, if the dynamic behavior of the axial settingdevice is known, it is simpler to use a simple time switch for limiting,in terms of time, the connection time of the negative voltage at theelectric motor.

Axial setting devices of the foregoing type, especially those whereinreinforced return springs or voltage reversing circuits effect a rapidreturn for the purpose of achieving a rapid disconnection of thefriction coupling, at the completion of the return motion, experience ahard jerk due to the balls hitting the groove ends of the ball groovesof the setting ring. This jerk is so pronounced that in a vehicle it isregarded as an unacceptable adverse effect on the comfort conditions inthe vehicle. Furthermore, if the driver is unprepared for such a jerk,it can make the driver feel insecure and cause him to regard the jerk asdamage to the vehicle.

It would be desirable to provide a new method for returning anelectromechanical axial setting device, especially for frictioncouplings.

SUMMARY OF THE INVENTION

The present invention provides a rapid return motion having a dampenedstopping behavior. Such an improvement is provided by a method wherein,during the return motion, shortly before the starting position isreached, the electric motor is short-circuited for the purpose ofgenerating a braking moment. Alternatively, a method is provided, duringthe return motion, shortly before the starting position is reached, apositive voltage is briefly applied to the electric motor. At the end ofthe returning process, shortly before the balls reach the end stops, themeans described here thus offer an electric braking method which can beachieved with very few additional switching mechanisms, while the basicmechanical configuration can remain unchanged.

A suitable device in accordance with the invention includes a rotationalposition sensor which is arranged at a rotating part, e.g. at the firstsetting ring and which, shortly before the balls reach the end stops inthe ball grooves, initiates the respective switching operation, i.e.either initiates short-circuiting or applies a positive voltage. In oneembodiment, it is also possible to replace the non-contact sensor byswitching contacts which, first, shortly before the end stops arereached, effect short-circuiting or the application of voltage andwhich, when the balls reach the end stops in the ball grooves,disconnect the electric motor. The means for dampening the stoppingeffect and for braking the returning electric motor constitute muchsimpler means than would be required by mechanical brakes and/or dampingdevices.

In a preferred embodiment, use is made of a permanently excited directcurrent motor.

Other advantages of the invention will become apparent upon reading thefollowing detailed description and appended claims, and upon referenceto the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this invention, reference shouldnow be made to the embodiments illustrated in greater detail in theaccompanying drawings and described below by way of examples of theinvention.

In the drawings:

FIG. 1 shows an inventive axial setting device in a first axial view.

FIG. 2 shows the device according to FIG. 1 in a section along line A—A.

FIG. 3 shows the device according to FIG. 1 in an axial counter viewrelative to FIG. 1.

FIG. 4 shows the device according to FIG. 1 in a section along line B—B.

FIG. 5 shows the device in the illustration according to FIG. 4, but ina plan view.

FIG. 6 shows a rotatingly drivable setting ring of the device in theform of a detail in an axial view of the grooves.

FIG. 7 shows the setting ring according to FIG. 6 in a sectional viewalong line A—A.

FIG. 8 shows a cylindrical section through a groove in an enlarged view.

FIG. 9 shows the detail X of FIG. 7.

FIG. 10 shows the detail Y of FIG. 7.

FIG. 11 shows the setting ring according to FIG. 6 in a perspectiveview.

FIG. 12 shows the second setting ring of the device according to FIG. 1in a plan view of the end face comprising the grooves.

FIG. 13 shows the setting ring according to FIG. 12 in a sectional viewalong line A—A.

FIG. 14 shows a cylindrical section through a groove in an enlargedview.

FIG. 15 shows the section B—B of FIG. 12.

FIG. 16 shows the setting ring according to FIG. 12 in a perspectiveinclined view.

FIG. 17 shows an inventive setting device used together with adifferential gear in a partial section.

FIG. 18 shows an assembly according to FIG. 17 in an axial view.

FIG. 19 shows different characteristics of an optimised disconnectionstrategy.

FIG. 20 shows the torque curve for the inventive disconnection strategyin connection with prior art strategies.

FIG. 21 shows the motor speed as a function of time for the inventivedisconnection strategy according to FIG. 20 as compared to strategiesaccording to the state of the art.

FIG. 22 shows the characteristic curves for the torque and engine speedas a function of time for an inventive braking strategy.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 5 will largely be described jointly. By way of a first flangeplate 12, an electric motor is bolted on to a bearing block 13 whichforms a second flange plate 14. In the bearing block 13, there issupported an extension of the motor shaft 15 which carries a firstpinion 16. In the bearing block 13, there is also supported an ancillaryshaft 17 which carries a further pinion 18 which engages the pinion 16and which, for the purpose of forming a reduction stage, carries afurther pinion 19. Via the bearing flange 14 the bearing block 13 issecured, for example, to a drive housing. A bearing sleeve 21 whose axisextends parallel to the motor axis is shown to include a flange plate 22which is rotatably supported in the drive housing. A first setting ring23 is supported on the bearing sleeve 21 by way of a radial bearing 24.The setting ring 23 includes a tooth segment 25. The pinion 19 of theancillary shaft 17 engages the tooth segment 25 of the first settingring 23. In parallel to the first setting ring 23, there is arranged afurther setting ring 26 which, by way of a holding lug 27, in arotationally fast way can engage the drive housing. Between the settingrings 23, 26, there is arranged a plurality of balls 29 which are heldin a cage 28 and by way of which the second setting ring 26 is centeredon the first setting ring 23. The first setting ring 23 is supported viaan axial bearing 31 on a disc 32 which is secured by a securing ring 33on the bearing sleeve 21. The second setting ring is supported via anaxial bearing 34 on a pressure plate 35 which is held by plate springpackages 36 in the flange plate 22. The pressure plate 35 simultaneouslyacts on pressure pins 37 which penetrate the flange plate 22. Ballgrooves in the setting rings 23, 26 holding the balls 29 are provided inthe form of ramps rising across the circumference in oppositedirections. The electric motor is shown to have cable connections 38,39. By driving the electric motor 11, the tooth segment 25 and thus thefirst setting ring 23 are rotated relative to the second setting ring 26which, via the holding lug 27, engages the drive housing and which, as aresult, is axially displaced against the returning force of the platesprings 36 and in consequence, loads the pressure pins 37. Furtherdetails as regards the functioning of the setting rings can be obtainedfrom the description of the following drawings.

A voltage reversing circuit 49 and a motor speed recording device 48 forthe electric motor 11 are logically connected to each other as afunction of the idling speed of the electric motor 11 in such a way thatthe voltage reversing circuit 49 is disconnected if, in the course ofthe device being returned, the idling speed of the electric motor isreached. The voltage reversing circuit applies either on positive ornegative voltage to the electric motor 11 as desired. The voltagereversing circuit 49 also acts as a short circuit switching assemblywhen short circuiting of the electric motor 11 is desired. Likewise, themotor speed recording device 48 operates as a rotational position sensorfor indicating a position of the setting ring.

FIGS. 6 to 11, again, will be described jointly below. The first settingring 23 with the tooth segment 25, in its end face, has five ballgrooves 41 which are circumferentially distributed at a pitch angle of72° and which each span a circumferential length of 58°. As can be seenin FIG. 8, the ball grooves, across the ring circumference, have ahelical angle of 1.5° and thus a variable depth between two stops 42 and43 for the balls 29. In the sectional view of the ball groove, the ballis shown in its two stopping positions in a dash-dotted line.

FIGS. 12 to 16 will also be described jointly below. In its end face,the second setting ring 26 includes five ball grooves 44 which arecircumferentially distributed at a pitch angle of 72° and span acircumferential length of 58°. The holding lug 27 with the guidinggroove 47 is clearly drawn. As can be seen in FIG. 14, the ball grooveshave a variable depth across the circumference due to a helical angle of1.5° and include two stops 45; 46 for the balls 29. One ball is shown indash-dotted lines in its two stopping positions.

The rising gradients of the ball grooves 44 in the second setting ring26 rise in the same direction as the gradients of the ball grooves 41 inthe first setting ring 23. As the setting rings 23, 26 are mounted insuch a way that their end faces containing the ball grooves 41, 44 faceone another, a relative rotation of the two setting rings relative toone another causes a ball 29 to roll so as to rise simultaneously inboth ball grooves 41, 44 or so as to descend simultaneously. The cageholds the balls in the ball grooves in positions which correspond to oneanother. A relative rotation of the two setting rings 23, 26 relative toone another in a first direction thus pushes the two setting rings 23,26 apart, whereas a relative rotation in the opposite direction allowssaid two setting rings 23, 26 to approach one another. The former isachieved entirely by driving the electric motor; the latter is achievedin particular by the returning force of the plate springs 36.

FIGS. 17 and 18 will be described jointly below. A setting device of theabove-mentioned type can be mounted in a differential drive 51. In thiscase, the bearing sleeve 21′ is integral with a differential carrier 52which is rotatably supported in the differential drive via rollingcontact bearings 53, 54. In the differential carrier 52, there aresupported two axle shafts 55, 56 which carry bevel gears 57, 58 whichengage differential bevel gears 59, 60. A friction coupling 61 includesfirst friction plates 63 which are connected in a rotationally fast wayto a sleeve 62 which is secured to an axle shaft 55, as well as twofriction plates 64 which are connected to the differential carrier 52 ina rotationally fast way. The friction coupling 61 is arranged between anaxially displaceable pressure plate 65 and a supporting member 66 fixedin the differential carrier 52. The pressure plate 65 can be loadeddirectly by the pressure pins 37′ which are displaced when the firstsetting ring 23′ rotates relative to the second setting ring 26′. Thesecond setting ring 26′ is held in a rotationally fast way by pins 67,68 which engage holding lugs 27 and which are secured in thedifferential drive housing 51. By rotating the setting ring 23 in afirst direction, the friction coupling 61 is closed, so that thedifferential drive develops a locking effect, whereas by returning thesetting ring 23, the friction coupling 61 is disconnected, so that thedifferential drive again becomes an open differential.

FIG. 19 shows the above-mentioned process of disconnecting a frictioncoupling with reference to various characteristics on a time axis. Thesecharacteristics are the torque transmitted by the friction coupling(torque transmitted), the current in the electric motor (current) andits rotor's rotational speed (rotational speed rotor). In the negativetime range, the setting device is shown in the outermost advancedposition. Starting from time 0.0, the setting device is returned asquickly as possible into the starting position, avoiding any stoppingjerks. In the negative time range, the current is characterised by pulsewidth modulation with rectangular jumps between 0 and approximately 25A. The torque transmittable by the friction coupling is constant atapproximately 2000 Nm. The rotational speed of the electric motorfluctuates with the frequency of the pulse width modulationapproximately around 0.

At the time 0.0, the electric motor is subjected to negative current(active disconnection), as a result of which the engine speed increasesto returning negative values, with the transmittable torque decreasingdue to the friction coupling being opened. After approximately 0.01seconds, the current is switched off, so that at the time of 0.015seconds, the current in the electric motor becomes 0. The disconnectionof the current (passive disconnection) has been chosen to be such that,approximately after the elapsed time, the motor reaches its nominalspeed of approximately 200 radian/sec., so that thereafter, due to theeffect of the plate springs, the speed can continue to increase inreturning. The transmittable torque continues to decrease up to a timeof 0.095 seconds. At that point in time, the electric motor isshort-circuited, so that, within the shortest possible time, ashort-circuit current reaches a value of approximately 45 A. As aresult, the speed of the motor, up to the time of 0.14 seconds, is againbraked to 0, as a result of which only slight overshooting occurs. Thetransmittable torque had already previously reached the value 0. As aresult of the braking process initiated by the electric motor, the ballsstop against the groove stops in a completely impact-free way.

FIG. 20 shows the torque curve (transmitted torque) of the frictioncoupling as a function of time as a result of the application ofnegative current (active “optimum”) being interrupted in accordance withthe invention, as compared to a permanent application of negativecurrent (active “standard”) and the return motion taking place entirelyas a result of spring force (passive). The return motion under springforce is referred to as being “passive”—it can be seen that such springforce effects the slowest decrease in transmittable torque. “Activestandard” refers to the permanent application of negative current to theelectric motor which, due to an internal voltage being induced, fromapproximately 0.04 seconds onwards, leads to a clear reduction in thetransmittable torque, whereas “active optimum” indicates the applicationof negative current which, after the idling speed has been reached, isinterrupted after approximately 0.04 seconds, which results in thequickest possible decrease in the transmittable torque.

For the three types of disconnection described in connection with FIG.20, FIG. 21 shows the curves of the returning speeds of the electricmotor (rotational speed rotor) as a function of time. The spread, interms of time, of the increases in rotational speed is responsible forthe above-mentioned torque decreases, with the speed 0 occurring whenthe balls reach the end stops in the ball grooves. In the case of thepermanent application of negative current (active standard), this takesplace at the latest point in time and especially much later than in thecase of the free (passive) return motion, whereas the short applicationof negative current (active optimum) in accordance with the inventivemethod leads to the balls reaching the stops in the quickest way, whichis characterised by the zero crossing of the speed curve accompanied bya related overshoot. The overshoot indicates the return motion of themotor as a result of jerk-like spring-back at the end stops in the ballgrooves.

FIG. 22 shows two processes which are similar to those shown in FIGS. 20and 21, i.e. the illustration of the transmittable torque (transmittingtorque) and the illustration of the motor speed in the case of thereturn motion (rotational speed rotor) and which refer to a furtheradvantageous control process which takes place directly prior to theballs reaching the end stops in the ball grooves.

The curves marked “active” refer to the torque and speed curvesresulting from the short application of negative current in accordancewith the process type “active optimum” according to FIGS. 20 and 21. The“active” curves show the steep decrease in the returning negative motorspeed to 0 and the overshoot to a clearly positive speed when the ballshit the stops in the ball grooves hard. The curves “active with shortcircuit” refers to the torque and speed curves under the influence ofelectric motor short-circuiting shortly before the balls hit the stops.The short-circuiting ensures early braking of the motor, so that thespeed is returned to 0 in a practically impact-free way. The undesirablehard impact of the balls against the ends of the ball grooves is thusavoided.

From the foregoing, it can be seen that there has been brought to theart a new and improved electromechanical torque control method andsystem having improved acceleration characteristics. While the inventionhas been described in connection with one or more embodiments, it shouldbe understood that the invention is not limited to those embodiments.Thus, the invention covers all alternatives, modifications, andequivalents as may be included in the spirit and scope of the appendedclaims.

What is claimed is:
 1. A method of controlling an electro-mechanicalaxial setting device wherein the axial setting device comprises: twosetting rings (23, 26) centered on a common axis, one of which isaxially held, with the other one being axially displaceably mounted, andone of which is rotationally fixedly held in a housing, with the otherone being rotatingly drivable, the two setting rings (23, 26), on theirrespective end faces facing one another, each comprise an identicalplurality of circumferentially extending grooves (41, 44), the grooves(41, 44), in a plan view of the end faces, comprise depths which rise inthe same circumferential direction, and form pairs of grooves (41, 44)in the two setting rings (23,26) each pair accommodating a ball (29),wherein the rotatingly drivable setting ring (23) is connected to anelectric motor (11), and the axially displaceable setting ring (26) isloaded by pressure springs (37) towards the axially held setting ring(23), the method comprising: applying a positive voltage to the electricmotor (11), to move the axial setting device into an advanced position;and for returning purposes, first applying a negative voltage to theelectric motor (11), and when the electric motor (11) has reached itsidling speed, disconnecting the motor from the negative voltage.
 2. Amethod according to claim 1 comprising, during the return motion,shortly before the starting position is reached, short-circuiting theelectric motor for the purpose of generating a braking moment.
 3. Amethod according to claim 1 comprising, during the return motion,shortly before the starting position is reached, applying a positivevoltage to the electric motor for the purpose of generating a brakingmoment.
 4. A method according to claim 2 comprising, during the returnmotion, when the axial setting device approximately reaches the startingposition, eliminating the short-circuiting at the electric motor (11).5. A method according to claim 3 comprising, during the return motion,when the axial setting device approximately reaches the startingposition, eliminating the positive voltage connection at the electricmotor (11).
 6. An electro-mechanical axial setting device, comprising:two setting rings (23, 26) centered on a common axis, one of which isaxially held, with the other one being axially displaceably mounted, andone of which is rotationally fixedly held in a housing, with the otherone being rotatingly drivable, the two setting rings (23, 26), on theirrespective end faces facing one another, each comprise an identicalplurality of circumferentially extending grooves (41, 44), the grooves(41, 44), in a plan view of the end faces, comprise depths which rise inthe same circumferential direction, and form pairs of grooves (41,44) inthe two setting rings (23,26) each pair accommodating a ball (29),wherein the rotatingly drivable setting ring (23) is connected to anelectric motor (11), and the axially displaceable setting ring (26) isloaded by pressure springs (37) towards the axially held setting ring(23), and a voltage reversing circuit for the electric motor and a motorspeed recording device for the electric motor which are logicallyconnected to one another via the idling speed of the electric motor forthe purpose of interrupting the voltage.
 7. An axial setting deviceaccording to claim 6 comprising a rotational position sensor arranged ata rotating part of the axial setting device for controlling of shortcircuit switching the electric motor.
 8. An axial setting deviceaccording to claim 6 comprising a rotational position sensor arranged ata rotating part of the axial setting device for controlling ofconnecting the electric motor to a voltage.
 9. An axial setting deviceaccording to claim 7 comprising a rotational position sensor forinterrupting the short circuit switching of the electric motor when arotational stop of the axial setting device in the starting position hasbeen reached.
 10. An axial setting device according to claim 8comprising a rotational position sensor for interrupting the connectionto a voltage of the electric motor when a rotational stop of the axialsetting device in the starting position has been reached.